Furnace



1935- w w. E. WEAVER 2,019,283

FURNACE 7 Filed Feb. 24, 1933 Patented Oct. 29, 1935 FURNACE William E. Weaver, Toronto, Ontario, Canada,

assignor to General Electric Company, a corporation of New York Application February 24, 1933, Serial No. 658,406 In Canada March 30, 1932 5 Claims. (Cl. 21911) My invention relates to furnaces, more par- ;icularly to furnaces useful in melting metals which are subsequently to be applied as a metal :oating to wire or the like.

My invention is particularly advantageous in :onnection with the process of coating wire or other like material, wherein the wire is passed continuously under rollers or guides immersed in a bath of molten metal. In such a coating procass it is a desideratum that the bath be kept at a substantially uniform temperature throughout. When no means is provided for substantially preheating the wire before entering the bath, it will be apparent that heat is taken from the bath by the wire and that the rate of heat exchange between the bath and the wire is greatest adjacent the point of entrance into the bath.

Further, whenever a dross is formed as the material to be coated passes through the bath, it ls desirable to remove the dross from the neighborhood of the material to be coated, in order that a clean coating may be applied thereto. When the dross is of greater specific gravity than the molten coating material it tends to sink to the bottom, but, if convection currents are present in the bath, the dross is not allowed to completely settle, remaining in partial suspension in the bath, and causing an imperfect coating to be applied to the material passing therethrough.

It is an object of my invention to provide a furnace of the type described and a method of coating wire or the like wherein heat is supplied to the bath at a greater rate adjacent the point where the material to be coated enters the bath, and wherein convection currents and consequent dross disturbance are substantially reduced.

It is a further object of my invention to provide an electrical heating system for a furnace of the type described which will provide for economic, easily controllable operation, and will result in an improved product.

One specific application of my invention is to an electric wire galvanizing furnace and in thefollowing, I will refer to this application, although it is obvious that my invention has other applications, and the use of my invention is desirable wherever, in metal coating practice, circumstances arise as hereinbefore set out.

For a more complete understanding of my invention reference should be had to the accompanying drawing in which Fig. 1 is a side view partly in section of a wire galvanizing furnace embodying my invention, Fig. 2 is an end viewalso partly in section of the furnace shown in Fig. 1 while Fig. 3 is a schematic Wiring diagram showing a preferred system of connections for the heating resistors embodying my invention. Referring now to Figs. 1 and 2 of the drawing, I have shown my invention in one form as comprising a heat resistance brickwork structure ll) supported by a metallic structure or framework II which structure encloses the bottom and side walls of a metal receptacle or tank l2 as well as forming a support for the tank. The top of the tank is open for the insertion and removal of the wire or the like to be treated into the molten metal in the tank. As shown the tank is of elongated rectangular form, the side walls of the tank being spaced from the surrounding brickwork structure IU to leave a heating chamber I3 at each side in which electric heating resistors are mounted on the brickwork structure.

The brickwork structure forming the heating chamber may be of any suitable construction well known in the art. As illustrated I have shown a composite structure made up of various types of heat resistant material such as firebrick, sil-o-cel brick and commonbrick, represented by the various hatchings, in order to take advantage of their respective economic heat-insulating characteristics.

The metal tank l2 which is intended to contain the molten metal, such as molten zinc, may be of any well known construction although I prefer to use a tank constructed along the lines indicated in Figs. 1 and 2, having two upright sides I4 and I5, and a flanged bottom member IS, the bottom member of the tank being turned upwardly at its ends, in order to form the vertical ends of the tank. The sides are secured to the flanges l'l of-the bottom member in any suitable manner, as by welding, riveting or hammer welding. In view of this construction I provide in the floor of the heating chamber two spaced longitudinal recesses l8, which are adapted to accommodate the down-turned flanges of the bottom member of the metal tank, allowing the flat portion of the bottom member to rest directly on the floor of the brick work structure In between the two spaced recesses.

The manner in which the wire to be galvanized is guided through the bath is diagrammatically indicated by the dotted lines in Fig. 2. A plurality of rollers or guides it are immersed in the bath of spelter adjacent each end of the tank l2. A plurality of wires 20 to be coated are passed under the rollers a short distance below the surface of the spelter, indicated at 2|, and pass in a longitudinal direction through the bath, The number and gauge of the wires being simultaneously galvanized and the speed and the length of travel through the bath determine the rate at which heat is taken from the bath by the wire.

In accordance with my invention I supply heat to the galvanizing bath adjacent the point of entrance of the wire at a greater rate than at points adjacent the remainder of its path through the bath. For purposes of reference, I term as the incoming zone that portion of the heating chamber adjacent the point of entrance of the wire into the bath and extending along the bath or tank for about two-thirds of its length, and the remainder the outgoing zone. As viewed in Fig. 1 I have assumed that the incoming zone is at the left-hand end and the outgoing zone at the right-hand end. As shown in Fig. 1, I mount in the incoming zone on each side wall of the heating chamber the resistor sections 22, 23 and 24, and in the outgoing zone the resistor sections 25, 26 and 21. The resistor sections 22, 23 and 24 are supplied with energy from one source and are arranged to deliver to the incoming zone a greater amount of heat per unit area than that delivered to the outgoing zone by the resistor sections 25, 26 and 27 which may be energized from the same or from a different source.

Further, in order to minimize the production of convection currents in the galvanizing bath, I

so choose the resistor sections 22, 23 and 24, that each delivers more heat per unit area than does the resistor section immediately below it. Resistor sections 25, 26 and 21 are also arranged in the same manner. In this way, I apply the greatest heat adjacent the path of travel of the wire through the bath, which ordinarily is but a short distance below the surface of the bath and in the zones heated by the resistor sections 22 and 25. Consequently, I minimize convection currents and the resulting dross disturbance.

The heating resistors 22 to 21 inclusive I have chosen to show as of the ribbon type although any other well known type of resistor which permits suitable heat distribution may also be used. As shown in Fig. 2 the heating resistors are mounted on the inner side walls of the brickwork structure In in the heating chambers I3 adjacent the side walls of the tanks. They are supported on the walls of the brickwork structure in any suitable well known manner, for example, on insulator refractories 30 preferably made of porcelain which are held or built into the wall of the brickwork structure. In accordance with one form of my invention I arrange the resistors in a plurality of rows one above the other, three rows being shown, the heating resistors in any one row being divided into two or more sections as, for example, sections 22 and 25 each section being separately energized as previously described.

In Figs. 1 and 2, I have shown suitable means such as outlet boxes 3 I, mentioned on the exterior of the brickwork structure, for permitting convenient connections to the resistor sections 22, 23, 24 and 25, 26, 21 which have terminals extending from the interior of the brickwork structure through the insulators 32 shown in Fig. 1.

A preferred system of connections for the resistors of Fig. 1 is shown in Fig. 3, where I have shown the resistor sections 22, 23 and 24 of the incoming zone connected in delta formation to a 3-phase power source 33 and the resistor sections 25, 2B and 21 of the outgoing zone connected in Y formation to a second 3-phase power source 34. Power sources 33 and 34 are preferably of different capacities, source 33 being the greater. In this way the elements of the resistor sections 22, 23 and 24 may be of greater thickness than otherwise and may consequently have an increased mechanical strength with a resultant longer life. It is to be noted also that in both circuits of Fig. 3 I may obtainbalanced 3-phase operation by the suitable selection of the resistance values of the resistor sections 22, 23, 24 and 25, 26 and 21.

In the final installation of a furnace embodying my invention, covers 35 are provided for the heating chambers I3, these covers extending between the heating tank l2 and the walls of the heating chambers. The covers 35 are preferably made in easily removable sections in order to permit ready access to any section of the heating chamber without disturbing any other sections, and are for the purpose of preventing air from entering or leaving the heating chamber. Suitable temperature controlling equipment is also provided to regulate the temperature of both the heating chamber and the molten metal by controlling the energization of the resistor sections. Such equipment which is well known in the art has not been shown in the drawing. For example, a control system may be used such as described and claimed in the Collins Patent No. 1,391,996, dated Sept. 27, 1921, two thermocouples responsive respectively to the heating chamber temperature and the temperature of the bath being provided.

In a typical wire galvanizing furnace constructed to embody my invention as above described, the circuit at the incoming zone comprising the resistors 22, 23, 24 was rated 150 kilowatts, 220 volts, 3-phase delta connected and the circuit at the outgoing zone comprising the resistors 25, 26, 21 was rated 54 kilowatts, volts, 3-phase Y connected. The incoming zone extended for two-thirds of the length of the tank and received about 39% more heat per linear foot than the outgoing zone. In each zone there were three rows of resistor ribbons, the upper row delivering 40% of the heat, the centre 33.3% and the lower 26.7%. The spelter, or molten zinc in the tank was covered with a two or three inch covering of a heat insulating material, known as Zonolite to reduce heat radiation therefrom, and the temperature was regulated within very narrow limits. Any suitable heat insulating material such as powdered sll-o-cel may be used for this purpose.

In the operation of this installation it has been found that the galvanized wire is of greatly improved and very uniform quality. This is due in part to the very close temperature control to which the furnace of my invention may be subjected, which results in uniform tensile strength, ductility, temper, elongation and zinc coating. In part also, the improved uniform quality of the product is due to the greatly reduced dros" formation and. dross disturbance which has been found to take place in this furnace.

As compared with fuel fired wire galvanizing furnaces a great reduction in dross formation has been noted, due partly to the close temperature control and partly to the nature of the heat distribution in the heating chamber. This results in a decreased expenditure of labor for drossing" as this operation will be required only at longer intervals.

By using a heat-insulating covering for the molten metal and covers for the heating chamber, heat radiation and conduction from the olten metal and from the heating chamber are aterially reduced, resulting in more efilcient eratlon and improved conditions in the operlng room.

The preferred structure of the tank, described ove, and the arrangement of the flanges of e tank in grooves in the floor of the heating amber has been found to greatly increase the e of the tank, due to the protection of the rivthrough the flanges from the direct heat of e resistor sections.

The nature of the heat distribution in the ing chamber has also resulted in marked adntages. In operation it has been found that a ry uniform temperature is obtainable in the elter, measured from end to end of the tank, 1d also measured from side to side of the tank. msequently in running a plurality of wires nultaneously through the bath in parallel relain, each wire is subjected throughout the igth of its travel through the bath to a subintially constant temperature which is the me for each wire. The resulting galvanized re is therefore of uniform quality throughout. What I claim as new and desire to secure by tters Patent of the United States, is:

1. In a furnace for coating wire with molten etal, a tank for containing a bath of molten etal, means for passing a wire to be coated rough said tank at a predetermined upper rel therein, and heating means associated with id tank for applying heat to the metal in said nk at a greater rate adjacent said predeterined level than adjacent a lower level to thereheat the molten metal in said upper level to a gher temperature than the metal in lower V618 and thereby minimize convection currents 1d consequent dross disturbance in the molten etal.

2. In a furnace for coating wire with molten etal, a tank for containing a bath of molten etal, means for passing wire to be coated rough said tank at a predetermined upper level erein, and heating means for applying heat to e metal in said tank adjacent the points of lmersion and emergence of the wire with spect to the bath, said heating means applying eat at a greater rate adjacent the point of imersion than adjacent the point of emergence thereby heat the wire passing into the bath 1d applying heat at a greater rate adjacent said edetermined level than adjacent a lower level the bath whereby dross disturbance is miniized.

3. In an electric furnace for coating wire with olten metal a heating chamber, a heat conicting tank within said chamber resting on the I01 of said chamber, said tank being adapted to contain a bath of molten metal, means for passing a wire to be coated through said tank at a predetermined upper level therein, and a plurality of heating elements having different rates of heat generation mounted at different 5 levels on the inner side walls of said heating chamber adjacent the sides of said tank, the heating elements having the greater rate of heat generation being uppermost and adjacent said predetermined level whereby heat is sup- 1o plied to said tank at a greater rate adjacent the path of the wire through said tank than adjacent a lower level in the tank to thereby heat the molten metal in said higher level to a higher temperature than the metal in said lower level whereby convection currents and dross disturbance in the bath are minimized.

4. -In an electric furnace for coating wire with molten metal a heating chamber, a heat conducting tank within said chamber for containing an a bath of molten metal, means for passing a wire to be coated through said tank at a predetermined upper level therein, and a plurality of groups of electric heating elements having different rates of heat generation mounted on the g5 inner side walls of said chamber adjacent said tank along substantially the entire length and height of said tank, said groups of heating elements having progressively lower rates of heat generation in the direction of movement of the wire through'said tank whereby heat is supplied at a greater rate to heat the cold wire entering the bath and the heating elements in each group having progressively decreasing rates of heat generation from said predetermined upper level, to a lower level to thereby heat the molten metal in said upper level to a higher temperature than the metal in said lower level whereby convection currents and dross disturbance in the bath are minimized. 0

5. In an electric furnace for coating wire with molten metal, a heat resistant heating chamber,

a heat conducting tank within said chamber, said tank comprising a flanged bottom member with upturned ends, and two flat side members, 

